Process of preparing acetic anhydride



Patented June 28, "1932 m'rsn STATES 1 PATENT OFFICE ERNST WINTER, OFCOLOGNE-QN-THE-RHINE-BRAUNSFELD, AND ALBERT Gm OF KNAPSACK; NEARCOLOGNE-ON-THE-RHINE, GERMANY, ASSIGNORS TO AK'I'IENGE- SELLSCHAFT FURSTICKSTOFFDURQER, OF KNAPSACK, NEAR COLOGNE-ON-THE- RHINE, GERMANY, 'ACORPORATION rnocuss or ranrmne ACE'L'IG hummus Ho brewing. Applicationfiled September 8, 1931, Serial No. 581,896, and in Germany February 15,19537.

The present invention relatesto a process of reparing acetic anhydride.

1 t is known that acetic anhydride may be made by treating a salt orsalts of acetic acid in a dry state with phosgene. The directmanufacture of acetic anhydride by causing phosgene to act uponaceticacid has hitherto been unknown. 1

Accordin to the resent invention acetic anhydride 1s made y treatingacetic acid with phosgene in the presence of a catalyst.

. As catalysts can be used compounds of metals whose chlorides aretransformed into acetates with elimination of hydrochloric acid whenheated with acetic acid, and whose acetates rather easily split offacetic acid. Qnly such metal compounds of the character described areoperative as are dissolved in heated acetic acid. Suitable catalystsare, for instance, compounds of the 2nd and 3rd groups of the periodicsystem, such as, for instance,

of magnesium, calcium, strontium, barium and aluminium; furthermorecompounds of the metals of the iron group and compounds of the fourthgroup of the periodic system and of the group of the rare earths, suchas compounds of cerium can be used. The catalyst may be used in the formof a salt of a mineral acid such as hydrochloric acid or in the form ofthe corresponding carbonate or as a salt of an organic acid such asacetic acid .or in the form of oxide.

:In the hitherto known processes of preparing acetic anhydride byreacting with phosgene upon solid salts of acetic acid it was only-withgreat difficulty that the reaction could be performed in a continuousmanner. ontrary thereto, our new process can easily be performed in acontinuous manner since as after the addition of the catalyst only lidenser whereby acetic anhyride and acetic acid are liquefied. Themixture is fractionated in a column which is connected .with thereaction vessel in such a manner that the acetic acid flows continuouslyback into the vessel.

The reaction can be performed at the boiling point of the acetic acid aswell as at lower temperatures from about 80 C. upwards such as fromabout 80 (ls-100 C. At any rate the temperature must be kept so highthat the metal compound is decomposed into the acetate. Furthermoreparticularly when working continuously one can start at the boilingpoint of acetic acid whereupon the temperature can be lowered down toest concentration, is mixed with about 10 per cent. of its weight ofanhydrous aluminium chloride. The mixture is heated to boiling andboiling is continued until the aluminium chloride is dissolved. Amoderate current of phosgene is then passed through the boilingsolution. in order to avoid losses of entrained acetic acid, thehydrochloric acid gas and carbonic acid gas which escape may be passedthrough coo acetic acid. When a quantity of phosgene suficient for thetransformation has been caused to react with the acetic acid, the wholeis kept boiling for some time in order to obtain the product as freefrom chlorine as possible. The anhydride, which is obtained in a goodyield, may be completely purified by distilling it in the usual manner.

2. Acetic acid is mixed as above indicated with about 10 per cent. of:its weight of anhydrous magnesium acetate, an. the mixture is heated toboiling until the magnesium acetate is dissolved. Phosgene is thenintroduced into the boiling solution until a sufiicient transformationinto acetic anhydride is effected. The further treatment is the same asindicated in Example 1.

' in 1.2 kg.

3. 50 g. of magnesium oxide are dissolved of glacial acetic acid andinto the solution after being heatedto boiling a current of 500 g. ofphosgene is slowly introduced. The further treatment isthe same asindicated in Example 1.

6. 100 g. of anhydrous ferric chloride are introduced into 1.2 kg. ofglacial acetic acid and into the mixture having been heated to boiling,900 g. of phosgene are slowly introduced, whereupon the resultingreaction product is distilled.

7. g. of lanthanum carbonate are dissolved in 1.2 kg. of glacial aceticacid and into the mixture heated to boiling there are introduced 900 g.of phosgene and the reaction mixture is worked up by fractionating.

8. 30 g. of yttrium oxide are dissolved in 1.2 kg. of glacial aceticacid and into the solution heated to 100 C. there are introduced 500 g.of phosgene. The reaction product obtained is freed from hydrochlor cacid by fractionating and then distilled in the usual manner.

9. 80 g. of anhydrous. nickel chloride are dissolved in 1.2 kg. ofglacial acetic acid an 900 g. of phosgene are introduced at 80 100 C.and the reaction product obtained is purified by distillation.

This application is a continuation in part of U. S. application SerialNumber 345,582 filed March 8, 1929.

We claim:

1. Theprocessofpreparingaceticanhydride which comprises treating aceticacid withphosgene in the presence of a metal compoun which is soluble inheated acetic acid and whose chloride when heated with acetic acid istransformed into the acetate, the treatment of the acetic acid withphosgene being effected at .a temperature at which the said metalcompouifl is decomposed into the acetate. I a

2. The process of preparing acetic anhydride which comprises treating ata temperature of between 80 C. and 100 C. acetic acid with phosgene inthe presence of a metal compound which is soluble in heated acetic acidandwhose chloride when heated with acetic in: l-nnnrvprnumnlq Mm Hmanntnta.

1 consistin 3. The new process which comprises treating boiling aceticacid with phos ne in the presence of a metal compound w 'ch is $01- ublein heated acetic acid and whose chloride when heated with acetic acid,is transformed into the corresponding acetate.

4. The new process which comprises treating acetic acid with phosgene inthe resence of a compound of a metal selected rom the group \consistingof the second and third group of the periodic system, which is solublein heated acetic acid and whose chloride when heated with acetic acid istransformed into the acetate, the treatment of the acetic acid withphosgene being effected at a temperature at which the said metalcompound is decomposed into the acetate.

5. The new process which comprises treating acetic acid with phosgene inthe presence of a salt of a metal selected from the group consisting ofthe second and third group of the riodic system, which is soluble inheated acetic acid and whose chloride when heated with acetic acid istransformed into the acetate, the treatment of the acetic acid withphosgene being eifected at a temperature at which the said metalcompound is decomposed into the acetate.

6. The new process which comprises treatin g acetic acid with phos enein the presence of a chloride of a meta selected from thegroupconsisting of the second and third group of the periodic s stem,which is soluble in heated acetic aci and whose chloride when heated wthacetic acid is transformed into the acetate, the treatment of the aceticacid with phosgene being efiected at a temperature at which the saidmetal compound is decomposed into the acetate. 7. The process ofpreparing acetic anhyd dride, which comprises treating boiling aceticacid with phosgene in the presence of aluminium chloride.

8. The process of preparing acetic anhydride, which comprises treatingboilin acetic acid withphosgene in the presence 0 10 per cent of itsweight of aluminium chloride.

9. The new process which comprises treating acetic acid with phosgene inthe resence of an oxide of a meta selected from t e group I of thesecond and third oup of the perio 'c system, which is soluble in heatedacetic acid and whose chloride when heated 4 with acetic acid istransformed into the acetate, the treatment of the acetic acid withphosgene bein effected at a temperature at which the sai posed into theacetate.

10. The new process which comprises introducing phosgene into boilingacetic acid in the presence of a metal compound which is soluble inheated acetic acid and whose chloride when heated with acetic acid istransformed into the acetate, lowering the temperature gradually down toabout 80 C. in the course metal compound is decom-v of fine reacticnadding the corresponding amount of acetxc acid and phosgene in the samedegree as the acetic anhydride is formed.

In testimony whereof, we 8, our signs.- 5 turcso ERNST NTER. ALBERT GR

